Radiation therapy or “radiotherapy” may be used to treat cancers or other ailments in mammalian (e.g., human and animal) tissue. One such radiotherapy technique is referred to as “gamma knife,” by which a patient is irradiated using a number of lower-intensity gamma rays that converge with higher intensity and high precision at a targeted region (e.g., a tumor). In another example, radiotherapy is provided using a linear accelerator (“linac”), whereby a targeted region is irradiated by high-energy particles (e.g., electrons, protons, ions, high-energy photons, and the like). The placement and dose of the radiation beam is accurately controlled to provide a prescribed dose of radiation to the targeted region. The radiation beam is also generally controlled to reduce or minimize damage to surrounding healthy tissue, such as may be referred to as “organ(s) at risk” (OARs). Radiation may be referred to as “prescribed” because generally a physician orders a predefined dose of radiation to be delivered to a targeted region such as a tumor.
Generally, ionizing radiation in the form of a collimated beam is directed from an external radiation source toward a patient. Modulation of a radiation beam may be provided by one or more attenuators or collimators (e.g., a multi-leaf collimator). The intensity and shape of the radiation beam may be adjusted by collimation avoid damaging healthy tissue (e.g., OARs) adjacent to the targeted tissue by conforming the projected beam to a profile of the targeted tissue.
The treatment planning procedure may include using a three-dimensional image of the patient to identify the target region (e.g., the tumor) and such as to identify critical organs near the tumor. Creation of a treatment plan may be a time consuming process where a planner tries to comply with various treatment objectives or constraints (e.g., dose volume histogram (DVH) objectives or other constraints), such as taking into account importance (e.g., weighting) of respective constraints in order to produce a treatment plan that is clinically acceptable. This task may be a time-consuming trial-and-error process that is complicated by the various organs at risk (OARs) because as the number of OARs increases (e.g., about thirteen for a head-and-neck treatment), so does the complexity of the process. OARs distant from a tumor may be more easily spared from radiation, but OARs close to or overlapping a target tumor may be more difficult to spare from radiation exposure during treatment.
Generally, for each patient, an initial treatment plan may be generated in an “offline” manner. The treatment plan may be developed well before radiation therapy is delivered, such as using one or more medical imaging techniques. Imaging information may include, for example, images from X-rays, Computed Tomography (CT), nuclear magnetic resonance (MR), positron emission tomography (PET), single-photon emission computed tomography (SPECT), or ultrasound. A health care provider, such as a physician, may use three-dimensional imaging information indicative of the patient anatomy to identify one or more target tumors along with the organs at risk near the tumor. The health care provider may delineate the target tumor that is to receive a prescribed radiation dose using a manual technique, and the health care provider may similarly delineate nearby tissue, such as organs, at risk of damage from the radiation treatment.
Alternatively or additionally, an automated tool (e.g., ABAS provided by Elekta AB, Sweden) may be used to assist in identifying or delineating the target tumor and organs at risk. A radiation therapy treatment plan (“treatment plan”) may then be created using an optimization technique based on clinical and dosimetric objectives and constraints (e.g., the maximum, minimum, and mean doses of radiation to the tumor and critical organs).
The treatment planning procedure may include using a three-dimensional image of the patient to identify the target region (e.g., the tumor) and to identify critical organs near the tumor. Creation of a treatment plan may be a time consuming process where a planner tries to comply with various treatment objectives or constraints (e.g., dose volume histogram (DVH) objectives), taking into account their individual importance (e.g., weighting) in order to produce a treatment plan that is clinically acceptable. This task may be a time-consuming trial-and-error process that is complicated by the various organs at risk (OARs) because as the number of OARs increases (e.g., up to thirteen for a head-and-neck treatment), so does the complexity of the process. OARs distant from a tumor may be easily spared from radiation, while OARs close to or overlapping a target tumor may be difficult to spare.
The treatment plan may then be later executed by positioning the patient and delivering the prescribed radiation therapy. The radiation therapy treatment plan may include dose “fractioning,” whereby a sequence of radiation therapy deliveries are provided over a predetermined period of time (e.g., 45 fractions or some other total count of fractions), such as with each therapy delivery including a specified fraction of a total prescribed dose. During treatment, the position of the patient or the position of the target region in relation to the treatment beam is important because such positioning in part determines whether the target region or healthy tissue is irradiated.